Andrew Devendorf has contacted Sen. Marco Rubio’s office every other day for the past month to beg the Florida Republican to make sure Congress’s final tax bill doesn’t make graduate school unaffordable for him and 179,000 other PhD students in the United States. Rubio has emerged as a potential swing vote on the tax bill, giving him possible leverage as Republicans finalize their plan with the goal of getting legislation to President Trump’s desk by Christmas.